Vehicle propulsion systems comprising hybrid powertrains are known for managing the input and output torques of various torque-generative devices, most commonly internal combustion engines and electric machines. One hybrid powertrain architecture comprises a two-mode, compound-split, electromechanical transmission which utilizes an input member for receiving torque from a torque-generative source, e.g. an internal combustion engine, and an output member for delivering motive torque from the transmission to a vehicle driveline. The internal combustion engine and first and second electric machines and the electromechanical transmission are selectively operative to transmit torque therebetween. The first and second electric machines are mechanically coupled to the internal combustion engine via an input shaft.
During operation of the hybrid powertrain, the internal combustion engine can be selectively deactivated, including incidences whereat the engine is unfueled and the engine crankshaft does not rotate. Rotational angle of the crankshaft is important when the engine is subsequently restarted, in part to accurately predict torque variations caused by cylinder compression during engine cranking prior to firing the engine. This is important because magnitude of variations in engine crankshaft torque and cylinder compression can be greatest during a first rotation of the engine.
Control systems for electric machines typically include a feedback device such as a position sensor, e.g., a resolver, to provide data to measure position and rotational velocity. On an electric machine comprising a three-phase multi-pole synchronous electric machine, precise and accurate measurement of position of a rotor relative to each of the poles of a stator is important to achieve efficient transmission of electrical energy. Rotor position is typically measured using the resolver. Position of the resolver relative to the machine rotor is subject to error due to factors including manufacturing variations and tolerances. Correction of the resolver position error relative to the machine rotor is correctable, and a method for accomplishing this is disclosed in detail in commonly assigned U.S. patent application Ser. No. 11/743901 (Attorney Docket No. GP-308283) entitled “Method and apparatus to Determine Rotational Position of an Electrical Machine”, which is incorporated herein by reference.
When using permanent-magnet synchronous machines, absolute position within one pole pair pitch is required. Also, the accuracy of this position measurement is critical, as it can affect the performance of the motor control, most noticeably in torque production and linearity. Using a resolver can provide precise position measurement. However, the accuracy of the measurement is directly affected by the initial alignment of the resolver during installation. The installation of the resolver and mechanical alignment can be difficult to control in production, and is typically addressed by employing a self-aligning start-up algorithm in the motor control. Furthermore, alignment of the resolver relative to the crankshaft of the attached internal combustion engine can be affected by initial installation of various components and by twisting occurring during operation.
There is a need to provide an improved method and system to precisely and accurately determine rotational angle of an engine crankshaft for use by a hybrid powertrain control system, to facilitate effective engine restart and for other reasons.